The British-based Observatory, which has a network of activists across Syria, reported four car bombs on Saturday.

Violence has risen in Syria particularly since rebels began to contest Assad's control around the capital and Syria's largest city Aleppo, but foreign powers remain deadlocked.

Western countries support the opposition but Russia, Syria's main arms supplier, and China have blocked three UN Security Council resolutions condemning Assad and reject sanctions on his government.

President Assad, whose family has ruled Syria for four decades, says he is fighting off radical Islamist militants funded by the West and Gulf Arab countries.

State television on Sunday said the army had been "eliminating al-Qaeda terrorists" in several suburbs surrounding Damascus including the rebel stronghold of Daraya.

The army entered part of Daraya, rebels said, a suburb on the southern outskirts of Damascus where fighters have launched mortars into the city. Rebel spokesman Abu Nidal said the army had entered one side of the town but that rebels were still in control of the rest of the area and were fighting back.

The army was firing heavy artillery and rockets into the town, rebels said.